1. Field of the Invention
The present invention relates to a knocking determination device and, more specifically, to a knocking determination device for an internal combustion engine that determines whether knocking occurred or not, based on a waveform of vibrations of the internal combustion engine.
2. Description of the Background Art
Conventionally, a technique for detecting knocking of an internal combustion engine is known. Japanese Patent Laying-Open No. 2001-227400 discloses a knock control device for an internal combustion engine that can accurately determine whether the engine knocks. The knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2001-227400 includes a signal detector detecting a signal representing a waveform of vibrations occurring in the internal combustion engine (or a vibration waveform signal), an occurrence period detector detecting a period as an occurrence period during which the vibration waveform signal detected by the signal detector assumes a predetermined value or higher, a peak position detector detecting a peak position in the occurrence period detected by the occurrence period detector, a knock determiner determining whether the internal combustion engine knocks based on the relation between the occurrence period and the peak position, and a knock controller controlling an operation state of the internal combustion engine in accordance with a determination result of the knock determiner. The knock determiner determines knock (knocking) occurs when the peak position relative to the occurrence period is in a predetermined range. The signal detector detects a prescribed frequency component particular to a knock signal as the vibration waveform signal.
According to the knock control device for an internal combustion engine disclosed in the publication, a signal representing a waveform of vibrations occurring in the internal combustion engine is detected by a signal detector. An occurrence period during which the vibration waveform signal assumes a predetermined value or higher and a peak position therein are detected by an occurrence period detector and a peak position detector, respectively. Thus, the knock determiner can determine whether the engine knocks by detecting the position of the peak in the occurrence period of the vibration waveform signal. According to the knock determination result, the operation state of the internal combustion engine is controlled. When the peak position relative to the occurrence period is in a predetermined range, that is, when a waveform has such a shape that the peak position appears earlier relative to a predetermined length of the occurrence period of the vibration waveform signal, the knock determiner recognizes it as being particular to knocking. Thus, even in a transition state where an operation state of the internal combustion engine abruptly changes or when electric loads are turned on/off, whether or not the internal combustion engine knocks is accurately determined, and the operation state of the internal combustion engine can be controlled appropriately.
While a frequency component particular to knocking is detected as the vibration waveform signal with the knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2001-227400, the frequency component particular to knocking is not constant. Accordingly, it is necessary to detect frequency components included in predetermined frequency bands. Thus, the detected frequency components may include those which are not particular to knocking. Such a problem is not considered in the knock control device for an internal combustion engine disclosed in Japanese Patent Laying-Open No. 2001-227400. Accordingly, some frequency bands may include great noise components. In this case, there has been a problem that the magnitude or peak of vibrations cannot be detected appropriately and the accuracy of knocking determination is deteriorated.